A lack of fruits and vegetables in the western diet could be the reason asthma rates are on the rise, a new study has found.

Researchers at the Lausanne University Hospital in Switzerland said gut bacteria ferments dietary fibres found in fruits and vegetables, and from that, fatty acids enter the blood stream, influencing the immune response in the lungs.

Using mice, the researchers fed the animals a standard diet with 4% fermentable fibres, or gave the mice a low-fibre diet comparable to the western diet, which contains no more than 0.6% fibre on average.

The mice were then exposed to dust mites and those on the low-fibre diet developed stronger allergic reactions and had much more mucus in the lungs than mice that ate the standard diet.

The researchers said the next step is to see if a diet enriched with fermentable fibres will affect those with asthma and allergies.